Lens blank and lap mounting for precision lens generating mechanisms



June ALJ. HOLMAN 2,377,344

LENS BLANK AND LAP MOUNTINGS FOR PRECISiON LENS GENERATING MECHANISMS Filed Dec. 12, 1941 2 Sheets-Sheet 1 June 5, 1945. A. J. HOLMAN 2,377,344

LENS BLANK AND LAP MOUNTINGS FOR PRECISION LENS GENERATING MECHANISMS Filed Dec. 12, 1941 2 Sheets-Sheet 2 Patented June 5, 1945 LENS BLANK AND m MOUNTING FOR rascrsroa LENS GENERATING Macmi- NISMS Arthnr 1.1mm, Brighton, N. Y. Application December 12, 1941, Serial in. 42am 3 Claims. (01. 51-55) My invention applies to precision lens grinding and polishing apparatus wherein the lap or polisher, as the case may be, and the work are rigidly supported with respect to the center of curvature of the surface being generated and both tool and work are so constrained that all movements thereof must take place about this center of curvature. Such mechanism is characterized by having one common center of oscillation and rotation about which boththe tool (lap or polisher) and the work must move and their movements are positively restricted to rotation and swinging (pendulum) motion. Apparatus of this type is fully described in my Letters Patent of the United States No. 1,827,748, dated October 20, 1931. The present /'structures, representing improvements in chuck-and tool designs and in means for mounting them, have been arrived at after long and careful testing of my lens generating apparatus in making large diameter long radius spherical surfaces. Lens grinding and polishing machines constructed according to the disclosure of the above mentioned patent and equipped with the tools and lens mounting means herein disclosed, are easily capable of producing consistently, in large volume and at low cost, spherical surfaces showing three color rings or less when tested with an accurate test plate.

Such extreme accuracy with present standard lens making equipment is now attained in large surfaces with difliculty and only by the most skilled workman, of whom there are too few. They employ hand operated apparatus and their output is totally inadequate to meet current demands. The structures presently to be described have increased the accuracy of performance of my former mechanism from three to fivefold and have doubled the production per machine, hence they are of importance in mass production of ultra precision optics.

My device may be best understood by reference to the accompanying drawings in which Fig. 1 is a view of my lens making apparatus.

Fig. 2 is a cross-section on line 22 of Fig. 1 showing the improved tooling.

Fig. 3 is a vertical section through the axis oi the inner and outer rotatable sleeves.

Referring now more specifically to the drawings in which like reference numerals indicate like parts. I is a base (Fig. 1) carrying the upright member 2 which supports the bracket 3 (Figs. 1 and 3) from which is rotatably supported the outer sleeve 4. A ring member 5 hingedly supported on outer sleeve 4 is rockable on the axis 6 which axis intersects at right angles the axis of rotation of outer sleeve 3. To ring member 5 is hingedly attached upper cage member I rockable on axis a-,a which axis also passes at right angles through the axis of rotation of outer sleeve 4 and through the axis 6. It is to be noted that the outer rotating sleeve 4, the rockable ring member 5, and the hingedly attached upper cage member I constitute a universal joint rotatable about and centered at the point of intersection of axis a-a, axis 6 and the axis of rotation of outer sleeve 4. Rods-l (Fig. 1), of which there are four (two showing) are fixed in upper cage member 1 at their upper ends and their lower ends are press fitted in lower cage member I. Between the upper and lower cage members I and 9 is slidably mounted the lap supporting member ill which may be fixed at any desired position within the cage by being clamped to rods I by any suitable means (not shown).

The cage supporting mechanism herein described permits rotation of the cage and oscillation of the same about the point where axis a-a and axis 6 intersect and, in the apparatus as constructed, suitable means are provided for rotating and oscillating the cage. A complete description of this mechanism is given in my Patent No. 1,827,- 748 hereinabove referred to.

The bracket 3 (Fig. 3) also supports an inner rotatable sleeve 30, a rocking ring member 3! and a hinged spindle supporting sleeve H, all so arranged as to permit rotation of the spindle l2 and oscillation of the same about the intersection of axis a-a and axis 6. The spindle I2 is arranged to slide with very slight clearance in its supporting sleeve H. The complete spindle supporting mechanism and the means for rotating and oscillating the same are likewise fully described in the above mentioned patent. Inas much as this application deals primarily with new tooling for this apparatus, it is believed that the above description of the machine is sufllcient for the present case.

Lap supporting member l0 (Fig. 2) has a centrally located threaded bore i3 square to its upper face H, the latter being square to the rods 8 of the cage, wherein lap supporting member l0 may be positioned at various elevations as previously described. The axis of threaded bore l3, if extended, would pass through the point of intersection or axis 0-11 and axis ii in the head of the mechanism. Permanently fixed in the face it of lap supporting member l0 and projecting slightly therefrom is hardened and ground contact ring I, the protruding surface thereof being concentric to threaded bore It and absolutely square thereto. The-lap It has integral threaded stud II which is centered and square to the body of the lap and fits with slight clearance in threaded bore I! thus serving to center the lap accurat-- ly in lap supporting member ID. Permanent? fixed in the lower surface of lap i6 is contact ring it, similar to contact ring l5, and its protruding surface is ground absolutely square to the axis of threaded stud H. A spanner wrench is used to screw the parts together and insure full contact between the hardened rings II and ll. 'lhediameterofthcsecontactringsispreferablyabout% oftbediameterofthelapand their contacting surfaces must be absolutely clean when the lap is mounted on the lap supporting member. The function of the contact rings is twofold, namely, to insure absolute squareness ofthelapwithrespecttotheaxisorthecageand to insure exact vertical positioning within the cage whenever the lap is replaced after having been removed. The abrading surface ll of the lap II is generated in the machine by the continually h ntin pattern of motion created as the mechanism operates, and when surface It is so formed it will be a portion of a true spherical n rface having its center at the common center of oscillation and rotation, namely. at the intersection of axis H and axis 0.

The smndle I 2 carries press fitted on its lower end the chuck carrier which isprovided with a large diameter annular contact surface II, the latter being ground square to the axis of spindle if. A recess 2! within the lower part of chuck carrier flis bored accurately to dimension and truly concentric to spindle I2 and a central bore 23 is threaded concentric thereto. A chuck 24 having a pilot projection 2| fitting with very slight clearance in recess 22 within chuck carrier II, is provided with a threaded central stud 26 to fit accurately within the threaded central bore 28 in chuck carrier 20. On chuck 24 and surrounding pilot projection 28 is annular contact surface 21 corresponding to annular contact surface II on chuck carrier 20, and it is'ground absolutely square to the axis of pilot projection II and to threaded stud 20. A fiexible gasket 2|, of uniform thickness, is placed between the parallel annular contact surfaces II on chuck carrier fl and I! on chuck 24. A lens blank 29 mounted centrally on the lower face of chuck 24 by means of suitable mounting pitch, will, upon operation of the machine wi h pr per abradin material upon the lap, acquire a spherical surface having its center of curvature at the point of intersection of axis 0-1: and aids I.

Prolonged experience with several models of my grinding and polishing machines organised as described in my Patent No. 1,827,748, wherein the work'and tool are both rigidly mounted with re pect to the common center of oscillation and rotation, proved that the mechanism would grind and polish several times faster than any'known machines or methods currently in commercial use. It was found, however, that in producing spherical surfaces to match an accurate test plate, there was considerable variation in the y of successive surfaces and, although most of the product was equal to or better than the better grades of commercial lenses, considerable improvement was required to produce continuously, surface after test plate within three color rings. .11; was discovered that, should the lap be removed from the machine and later replaced therein, a tilt of one-ten-thousandth of an inch from one side of the lap to the other would make a decided difference in the curvature of the surface generated by the lap on the lens blank. It was also discovered that, after a surface was ground and polished with the machine organized as described in my patent, the mere operation of loosening the set screw in the hub to remove the chuck from the machine for cleaning and testing the work, would cause a decided astigmatic distortion in the finished surface. These experiences pointed surface, which would match the outthencedforlmplvvedlapandchuckmonntlnsl.

involvcsthreeprecision fits which must operate simnltaneousb: namely,

2| and i'lmustbehadtosecureexactsquareness of the chuck 2| with spindle II. It was found that a rubber gasket placed between annular surfaces fl and I! cushioned thel regularities forced into thisflnal ilt bythesimultaneous fits ofthread in thread and pilot in recessbore, tosuchadegree that spherical surfaceaftersurfaoecouldbegroundandpolishedandeachwould show substantially the same color pattern when examined imder the test plate and none of the surfaces showed any signs of stigmatinn.

My grindingandpolishingmachine organined to control rigidly all movemenisoftooland work from the common center oi'oscillation and rotation; asfully described inmypatent hcreinbefore referred to, when equippedwiththeaccuratelyiittingstructureshereindiscloeed,a-refullycapable of producing the ultrapreeiseopticalmrfacesrequired in the highest grade'telescopeand photographic objectives. Moreover, these surfaces can beproducedingreatquantitiesatsreatlyrcduced cost by newly trained and rdatively unskilled operators. 'lhetimereqmredtogm'ateafinished accurate spherical surface on my mechanism,aspresentlyorganiaed,isfrom /sbi'wof the time required to produce the same accuracy bycurrentlycommercialmachinesandpmoo-es.

whiielhavedescribedmyimprovedtoolhnas applied in amechanism forgrindingandpolhhing spherical lenses, wherein all ofthe work and tool (lap or polisher) are rigidb controlled from a common center of oscillation and rotation,itwillbereadib pparenttothoseskiiled intheartthattheidentical'toolingmaybemed to advantage in any lens making wherein the movementsofworkandtoolare rigidly controlled. Obviously, m lap mounting means and the chuck carrier and chuck are elementsofthelinkagebetweenthecentemoranes, ofrigidcontmlofmotionandthesurfacehein generated, hence they must be extremely well fitted to make possible their essentialb precise replacementinoperatingposition. Inamechanism formaklngoptical fiats (sphericalsurfacesofinfinjteradius) theworkandtoolmlghtberigidly controlled to oecillateand rotate about fixed and/or moving parallel axes, andinsuchadevice the tooling herein describedwouldbeequallyeffective. Itisconceivablealsotlntrigidlycontrolled movements might be used eifcctively in generatingtorlcsudamorasmerlcaisnrfaceaof revolution, or any other type of optical surface produceable by machine. Claims appended hereto are drawn, therefore, to cover any and all applications of this invention in suchmechanism and they are intended to be so interpreted.

Having thus fully described my invention, its application and functioning, what I claim is:

1. In a lens grinding mechanism wherein the abrading movements are rigidly controlled from fixed and moving axes, a lap supporting member and a lap, each provided with coacting elements adapted and arranged to bring the center of curvature of the lap surface in exact register with the common center of oscillation and rotation. said coacting elements comprising closely fitted threaded bore and threaded stud for precisely centering and for holding said lap on said lap supporting member and precision means for exactly squaring said lap to said lap supporting member as said threaded parts are finally tightened, said means including contact rings inserted in said lap and said lap supporting member.

2. In a device of the character specified, a lap supporting member, a lap having a spherical abrading surface, and dual simultaneously functioning fits between said lap supporting member and said lap, said-fits comprising an accurate thread in thread fit for centering said lap on said lap supporting member and retaining the same securely attached thereto, and inserts in said lap and said lap supporting member adapted and arranged to provide a parallel annular surface to surface fit of considerably greater minimum diameter than said thread in thread fit, for squaring said lap to said lap supporting member and fixing accurately the position of said spherical abrading surface with respect to said lap supporting member 3. In a lens generating mechanism wherein the abrading movements are rigidly controlled from the common center of oscillation and rotation, a central spindle suitably supported within said mechanism so that it may swing and rotate about said common center and may feed axially away from said common center, a chuck carrier fixed securely on said spindle, a chuck whereon a lens blank may be mounted, a flexible gasket, and triple pairs of simultaneously cooperating elements on said chuck carrier and on said chuck adapted and arranged to (a) hold said chuck securely to said chuck carrier, (b) positively center said chuck thereon, and (c) positively square said chuck to said chuck carrier and to said spindle, said flexible gasket being so positioned between said chuck carrier and said chuck as to absorb the residual errors in said triple pairs of simultaneously cooperating elements.

4. In a device of the character specified, a spindle, a chuck carrier securely fixed on said spindle. a chuck adapted and arranged to support a lens blank, and a flexible gasket, said chuck carrier and said chuck being provided with three independent but simultaneously functioning precision fits including a thread in thread fit, a pilot in bore fit, and annular parallel surface to surface fit, said flexible gasket being positioned between said annular parallel surfaces to absorb all residual errors accumulated at this third and final simultaneously functioning fit.

5. In a device of the character specified, the combination of a lap supporting member. a lap having a spherical abrading surface, dual simultaneously functioning fits between said lap supporting member and said lap adapted and arranged to center said lap on said lap supporting member, to securely attach and square said lap thereto, and to fix precisely the position of said spherical abrading surface with respect to said lap supporting member, a spindle, a chuck carrier rier, said flexible gasket being adapted and ar-,

ranged to absorb all residual errors accumulated at the third and final fit of said chuck on said chuck carrier. I

6. In a lens generating mechanism wherein the abrading movements are rigidly controlled from the common center of oscillation and rotation, the combination of a rotatable universal joint, a We supported rigidly from said universal Joint, a lap supporting member adjustably positioned within said cage, a lap, and cooperating means on said lap supporting member and on said lap adapted and arranged to permit repeated removal and subsequent replacement of said lap in such position within said case that the center of curvature of the abrading surface on said lap will coincide with said common center of oscillation and rotation, said cooperating means comprising a central threaded stud on said lap which fits precisely in a threaded bore in said lap supporting member and opposed inserts in said parts arranged to square said lap on said lap supporting member and to determine the exact elevation of the abrading surface of said lap in said cage.

7. In a lens generating mechanism wherein the abrading movements are rigidly controlled from fixed and moving axes, the combination of a 9 supporting member, means for rigidly suspending said lap supporting member so that it may have freedom of movement only with respect to oscillation and rotation about said fixed and moving axes, a lap carried on said lap supporting member, and cooperating means on said lap supporting member and on said lap adapted and arranged to permit repeated removal and subsequent replacement of said lap in such position on said lap supporting member that the abrading surface of said lap will coincide exactly with its former position with respect to said fixed and moving axes, said cooperating means comprising a central threaded stud on said lap which fits precisely in a threaded bore in said lap supporting member and opposed inserts in said parts arranged to square said lap on said lap supporting member.

8. In a surface generating mechanism wherein a fixed relation of the tool with respect to the center and axes of oscillation and rotation must be rigidly maintained and wherein the tool must be removed repeatedly and returned subsequently to its exact former position, the combination of a lap supporting member, a lap, and means adapted and arranged to provide dual simultaneously functioning fits between said lap supporting member and said lap, said means comprising an integral central threaded stud and contact ring on said lap, and corresponding precision threaded bore and inserted contact ring on said lap supporting member.

ARTHUR J. HOLMAN. 

